LED drive circuit

Abstract

An LED drive circuit comprises a power supply unit, a first LED lamp string, a first voltage control unit, a second LED lamp string and a first power transfer unit. The power supply unit outputs a drive power to drive the first LED lamp string. The first voltage control unit gets the drive power and stabilizes and provides the voltage to the first LED lamp string. The first voltage control unit includes a power switch where the drive power generates a power loss. The second LED lamp string and first power transfer unit are coupled in series with the first voltage control unit so that the power loss is transferred and output to drive the second LED lamp string. Thus loss of the drive power is reduced and lighting efficiency of the LED improves.

What is claimed is: 
     
       1. An LED drive circuit, comprising:
 a power supply unit including an output end to output a drive power; 
 a first LED lamp string which is connected to the output end of the power supply unit and driven by the drive power and includes a first anode end connecting to the output end and a first cathode end, wherein the first LED lamp is coupled in parallel with a first capacitor and a first resistor to filter out ripple waves; 
 a first voltage control unit which is connected to the first cathode end to get the drive power and stabilize and provide a voltage to the first LED lamp string and includes a control end connected to the first cathode end, a feedback end, a power switch connected to the control end and the feedback end and a control circuit connected to the power switch, the drive power generating a power loss at the power switch, the control circuit including a third resistor which bridges a gate and a drain of the power switch, a voltage stabilization element which is connected to the gate of the power switch, a fourth resistor which is connected to an emitter of the voltage stabilization element and a fifth resistor which is connected to a gate of the voltage stabilization element; 
 a second LED lamp string connecting to the control end of the first voltage control unit via a rectification diode; and 
 a first power transfer unit coupling in series with the second LED lamp string and connected to the feedback end of the first voltage control unit; 
 wherein the first power transfer unit transfers and outputs the power loss generated on the power switch to the second LED lamp string to drive the second LED lamp string. 
 
     
     
       2. The LED drive circuit of  claim 1 , wherein the second LED lamp string is coupled in parallel with a second capacitor and a second resistor. 
     
     
       3. The LED drive circuit of  claim 1 , wherein the first voltage control unit includes a Zener diode connected to the power switch to provide voltage stabilization protection for the power switch. 
     
     
       4. The LED drive circuit of  claim 1 , wherein the voltage stabilization element is selected from the group consisting of an NPN transistor, a PNP transistor, an operational amplifier, serial-connected diodes and a Zener diode. 
     
     
       5. The LED drive circuit of  claim 1 , wherein the first power transfer unit is formed in a circuit structure the same as that of the first voltage control unit. 
     
     
       6. The LED drive circuit of  claim 5  further including a first expansion unit which is connected to the first power transfer unit and formed in a circuit structure the same as that of the second LED lamp string and the first power transfer unit. 
     
     
       7. The LED drive circuit of  claim 1 , wherein the first power transfer unit includes a resistor. 
     
     
       8. The LED drive circuit of  claim 1 , wherein the power switch is selected from the group consisting of an N-type power switch, a P-type power switch, an NPN transistor and a PNP transistor. 
     
     
       9. The LED drive circuit of  claim 1  further including a second voltage control unit and a second power transfer unit, the second voltage control unit and the second power transfer unit being coupled in parallel with the first voltage control unit and the first power transfer unit.